Electrolytic process of making chlorine



Dec. 2, 1969 FUMIO HINE ETAL 3,481,847

ELECTROLYTIC PROCESS OF MAKING CHLORINE Filed Sept. 16, 1965 VOL 75 /0 100 L06 CURRENT oe/vs/rv (am/m AGENT United States Patent 3,481,847 ELECTROLYTIC PROCESS OF MAKING CHLORINE Fumio Hine, Takaishi-cho, Senhoku-gun, Osaka, Zenichiro Takehara, Ukyo-ku, Kyoto, and Shiro Yo'shizawa, Sakyo-ku, Kyoto, Japan, assignors to Oiin Mathieson Chemical Corporation Filed Sept. 16, 1965, Ser. No. 487,752 Claims priority, application Japan, Sept. 21, 1964, 39/ 54,698 Int. Cl. C01b 7/06 US. Cl. 204-128 7 Claims ABSTRACT OF THE DISCLOSURE In the electrolysis of aqueous hydrochloric acid, an oxygen-depolarized cathode is immersed in a catholyte containing a chloride or oxide of Cu, Ag, Au, Fe, Co, Ni, 'V, Cr or a rare earth element having an atomic num her from 57 to 71 inclusive. Chlorine is produced at the anode.

This invention relates to improvements in the manufacture of chlorine by electrolysis of hydrochloric acid. More particularly this invention relates to a process in which hydrochloric acid is electrolyzed between an anode at which chlorine is evolved and an oxygen-depolarized cathode at which water is formed. In order to depolarize the cathode, an oxygen-bearing gas is supplied in contact with the cathode, either internally or externally of the cathode, and the hydrogen chloride electrolyte contains from 0.001 to 1 gram mole per liter of a chloride or oxide of Cu, Ag, Au, Fe, Co, Ni, V, Cr or a rare earth element having an atomic number from 57 to 71 inclusive. The rare earth elements of this group are lanthanum, cerium, praseodymium, neodymium, promethium, sarnarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

Suitably the hydrogen chloride concentration in the anolyte and catholyte is from 5 to 25 Weight percent. At lower hydrogen chloride concentrations the electrolysis is inefficient and at concentrations above 25 percent the evolved chlorine is contaminated with increasing concentrations of hydrogen chloride gas.

The cathode is depolarized by means of an oxygencori'taining gas introduced into the catholyte in contact with the cathode. The oxygen-containing gas is preferably air-but may suitably be oxygen-enriched air containing, for example, 50 percent, 90 percent or 95 percent oxygen or it may be pure oxygen. The oxygen-containing gas is suitably introduced into the catholyte, preferably in the? lower portion thereof to promote contact with the catholye. Alternatively and preferably the cathode is constructed of gas-permeable material and appropriately has a hollow core. The oxygen-containing gas is introduced internally of the cathode and flows through the gas-permeable walls of the cathode.

The anolyte and catholyte are connected through an ion-permeable diaphragm, for example, asbestos cloth, asbestos paper, or polymeric materials having ionic substituents. The diaphragm suitably has two extended dimensions arranged between the anolyte and catholyte chambers.

The porous cathode is suitably constructed of graphite or' other forms of porous carbon. Porous forms of platinum or other corrosion-resistant metals are suitable. These porous metal cathodes may be formed by pressing or sintering the powdered metals or by other known means.

It is known in the prior art, for example, in US. Patent 2,273,795 issued Feb. 17, 1942 to Heise et al., assignors 3,481,847 Patented Dec. 2, 1969 to National Carbon Company, particularly at page 3, column 2, lines 33-47 to electrolyze sodium chloride brine introducing air or oxygen through a porous carbon cathode into the cell to depolarize the cathode and to reduce the power consumption of the cell. Also at page 2, column 2, lines 48-66, the patent discloses the electrolysis of copper chloride solutions having sodium chloride added thereto, the cuprous chloride formed in the process acting as an anodic depolarizer to reduce the required cell voltage. In contrast, the process of the present invention uses metal chlorides or oxides which are unexpectedly efiective as cathodic depolarizers in the electrolysis of hydrochloric acid. In addition, the depolarizers of the present invention are used as catalysts rather. than intermediates or reagents in a leaching process.

US. Patent 2,097,077 issued Oct. 26, 1937 to Oppenheim discloses air-depolarized electrodes in electric batteries having aqueous electrolytes. These are for the purpose of generating an electric current in contrast to the process of the present invention in which an electric current is imposed on an electrolyte for the purpose of producing chlorine.

FIGURE 1 shows a system for carrying out the process of the present invention. FIGURE 2 shows graphically the results obtained in the operation of the processes described in Example I.

In FIGURE 1, cathode 1 is suspended in catholyte chamber 9C and anode 2 is suspended in anolyte chamber 9A. The electrodes are connected to a source of current 10. The anolyte and catholyte chambers are joined through asbestos diaphragm 3. Oxygen inlets to the catholyte chamber are provided at 6 or 6. When cathode 1 is composed of solid graphite, oxygen inlet 6, fitted with nozzle 5, is used for the introduction of oxygenbearing gas and inlet 6' is appropriately omitted. When cathode 1 is composed of gas-permeable graphite and has a hollow core, oxygen inlet 6 is used for the introduction of the oxygen-bearing gas and inlet 6 is appropriately omitted. Chlorine outlet 7' is provided from the anolyte chamber 9A. Outlet 7 is provided from the catholyte chamber 9C for the removal of excess oxygen-bearing gas and water vapor.

Separate circulating systems are provided to maintain the concentration of anolyte and catholyte. Continuously or intermittently, anolyte is withdrawn from anolyte chamber 9A via line 11 by pump 12 and transferred via line 13 to absorber 14. Hydrogen chloride in the form of gas or concentrated hydrochloric acid is introduce-d via line 15 into absorber 14. The fortified anolyte is transferred via line 16 to anolyte cham-ber 9A.

Catholyte is removed from catholyte chamber 9C via line 17 by pump 18 and transferred via line 19 to absorber 22. Hydrogen chloride in the form of gas or concentrated hydrochloric acid is introduced via line 20 into absorber 22. In addition, makeup catalyst as necessary is introduced via line 21 into the absorber 22. The thus fortified catholyte is returned via line 23 to catholyte chamber 9C.

FIGURE 2 presents the results of the operations described in Example 1. Electrolysis of hydrochloric acid was performed in the presence of various catalysts of the invention and, for comparison, in the absence of added catalyst. In FIGURE 2, curve (1) shows the decrease in electrode potential in volts which increasing current density due to polarization of the cathode when no catalyst is present in the catholyte. Curves (2), (3), (4), (5) and (6) show the electrode potential in volts using V 0 La O FeCl CuCl and CrO respectively, in the concentrations shown in Table 1, at various curtent densities. The improvement in the electrode potential 3 compared to the blank (1) is shown in FIGURE 2, particularly in the case of CrO where the electrode potential is maintained even at high current densities.

EXAMPLE I A cell was constructed having a solid graphite anode in an anolyte chamber and a solid graphite cathode in a catholyte chamber. The two chambers were connected by a tubular bridge containing an asbestos fiber diaphragm. Suitable tubes permitted the removal of chlorine from the anolyte chamber, the introduction of oxygen gas at a point in the catholyte chamber directly below the cathode and the removal of excess oxygen and Water vapor from the catholyte chamber. Both chambers were filled with 2-normal hydrochloric acid and direct currents of varying voltages were applied to the electrodes. Oxygen was introduced below the cathode and contacted the surface of the cathode. Chlorine was evolved at the anode and was removed from the anolyte chamber. Currents and voltages were measure-d, current densities were calculated and voltages were referred to the hydrogen electrode. A curve was drawn by plotting current densities against voltages and appears as curve 1 in FIGURE 2.

The above procedure was repeated, removing the catholyte and replacing it with 2-normal hydrochloric acid containing various metal compounds in the concentration shown in Table I.

TABLE I.2-NORMAL HYDROCHLORIC AC YD \VIlII METAL COMPO UNDS Concentration,

Metal Compound moles per liter Curve No. (FIG. 2):

EXAMPLE II The procedure of Example I was repeated using a hollow, gas-permeable graphite cathode through the walls of which oxygen was passed into the catholyte. The results essentially duplicated those of Example 1.

EXAMPLE HI An apparatus essentially as shown in FIGURE 1 with a solid graphite anode and a hollow gas-permeable graphitecathode was operated by charging 20'percent hydro chloric acid to both catholyte and anolyte chambers. The anolyte was continuously circulated from the anolyte chamber, fortified by introduction of 32 percent hydrochloric acid to maintain a concentration in the anolyte of 20 percent HCl and the fortified anolyte was returned to the anolyte chamber. The catholyte was similarly circulated continuously from the catholyte chamber, fortitied with 32 percent hydrochloric acid, chromic acid was introduced as necessary to maintain a concentration in the catholyte of 0.05 mole per liter of CrO and the fortified catholyte was returned to the catholyte chamber. Air was supplied through the walls of the hollow air-permeable cathode and a current density of 10 milliamperes per square centimeter was maintained on the cathode. The voltage of the cell was 1.3 volts at this current density. The temperature of the electrolyte was C. Chlorine gas was produced from the anolyte chamber.

What is claimed is:

1. In a process for electrolyzing aqueous hydrochloric acid to produce elemental chlorine wherein an electric current is passed between an anode immersed in an aqueous anolyte and a cathode immersed in an aqueous catholyte, said anolyte and catholyte being connected through an ion-permeable diaphragm, maintaining a concentration in said anolyte and catholyte of 5 to 25 weight per cent of hydrogen chloride, the improvement of maintaining a concentration in said catholyte of 0.001 to 1 gram mole per liter of a chloride or oxide of Cu, Ag, Au, Fe, Co, Ni, V, Cr or a rare earth element having an atomic number from 57 to 71 inclusive, continuously introducing an oxygen-containing gas into said catholyte in contact with said cathode and removing elemental chlorine from said anolyte.

2. A process according to claim 1 in which the concentration of hydrogen chloride is maintained by removing portions of said anolyte and catholyte from the zone of electrolysis, fortifying the hydrogen chloride content of said anolyte and catholyte by adding thereto a hydrogen chloride containing feed material having a greater concentration of hydrogen chloride than the thus removed portions of anolyte and catholyte and returning the thus fortified anolyte and catholyte to the bodies of anolyte and catholyte remaining in the zone of electrolysis.

3. A process according to claim 2 in which the hydrogen chloride containing feed material is concentrated aqueous hydrochloric acid containing 32 to 36 weight percent hydrogen chloride.

4. A process according to claim 2 in which the hydrogen chloride containing feed material is hydrogen chloride gas. a

5. A process according to claim 1 in which said oxygencontaining gas is distributed into the lower portion of the catholyte.

6. A process according to claim 1 in which said oxygencontaining gas is passed into said catholyte through the walls of a cathode having gas-permeable walls.

7. A process according to claim 1 in which said oxygencontaining gas is air.

References Cited UNITED STATES PATENTS 2,468,766 5/1949 Low 204-128 2,666,024 1/1954 Low et al. 204-428 3,119,757 1/ 1964 Schroeder 204-128 3,129,152 4/1964 Teslte et al. 204-428 3,291,708 12/1966 Juda 204-428 1 FOREIGN PATENTS 701,506 1/1 965 Canada. 303,027 10/ 1929 Great Britain.

JOHN H. MACK, Primary Examiner H. M. FLOURNOY, Assistant Examiner U.S. Cl. X.R. 204129 

